1. Field of the Invention
The present invention relates to a wavelength discriminating function, and more particularly to a wavelength division multiplexing transmission device and method having a wavelength discriminating function applicable to a wavelength division multiplexing transmission system in an optical communication system.
Recently, there has been considerable activity of increasing communication channels due to an abrupt demand for communications in optical transmission systems. However, an extension work of optical fiber cables needs a huge amount of cost. Hence, a wavelength division multiplexing transmission system is positioned as a key scheme because such a system efficiently utilizes the existing optical fiber cables and can increase the channel capacity by increasing the degree of multiplexing. Nowadays, four-wave multiplexing, eight-wave multiplexing, 16-wave multiplexing and 32-wave multiplexing have been used in practice in the wavelength division multiplexing transmission system.
2. Description of the Related Art
FIG. 1 is a block diagram of a conventional wavelength division multiplexing transmission system (four-wave multiplexing). Line terminal equipment LTE receives four data signals STM-M of a relatively low bit rate and multiplexes the data signals into an optical signal STM-N of a relatively high bit rate having a given wavelength by a method which will be described with reference to FIG. 2.
A line terminal equipment (LTE) 11 multiplexes 1 multiplexes four data signals STM-M#1-#4 of a relatively low bit rate into a single optical signal STM-N of a relatively high bit rate having a wavelength xcex1 to an optical coupler 15. Similarly, line terminal equipment LTE 12, 13 and 14 respectively output multiplexed optical signals STM-N having wavelengths xcex2, xcex3 and xcex4 and supply them to the optical coupler 15, which has a wavelength multiplexing function (MUX).
The wavelengths xcex1-xcex4 are arranged as shown in FIG. 3. As shown in FIG. 3, the wavelengths xcex1-xcex4 are respectively set equal to 1548.51 nm, 1551.72 nm, 1554.94 nm and 1558.17 nm. With this arrangement, the wavelength division multiplexing can be realized. Further, 8-wave multiplexing and 16-wave multiplexing can be realized as shown in FIG. 3.
Turning to FIG. 1 again, the optical coupler 15 combines the four high-bit-rate optical signals STM-N having the different wavelengths from the line terminal equipment 11-14, and outputs a combined, namely, multiplexed optical signal to an optical coupler 17 via an optical fiber cable 16.
The optical coupler 17, which has a wavelength demultiplexing function (DMUX), demultiplexes the multiplexed STM-N signal received from the optical fiber cable 15 into four optical signals STM-N having the different wavelengths. Then, the optical coupler 17 outputs the optical signal STM-N of the wavelength xcex1 to line terminal equipment LTE 18. Similarly, the optical coupler 17 outputs the optical signals STM-N of the wavelengths xcex2-xcex4 to line terminal equipment LTE 19-21, respectively.
The line terminal equipment 18 is supplied with the high-bit-rate optical signal STM-N of the wavelength xcex1 and demultiplexes it into four low-bit-rate data signals STM-M by a method which will be described later with reference to FIG. 2. Similarly, the line terminal equipment 19, 20 and 21 are respectively supplied with the high-bit-rate optical signals STM-N of the wavelengths xcex2-xcex4 and demultiplex them into four low-bit-rate data signals STM-M.
The line terminal equipment LTE will be described with reference to FIG. 2, which is a block diagram thereof. The line terminal equipment 11 receives the four low-bit-rate data signals STM-M#1-STM-M#4 from an external device, and outputs these signals to a multiplexer (MUX) 29 via interface parts 25-28, respectively. The multiplexer 29 inserts OHBs (Over Head Bit or Over Head Byte), which are used to transfer maintenance information between communication devices.
A system controller 30 performs various control procedures in accordance with information and data supplied from a local terminal 33 and/or a remote terminal 23 such as a workstation (WS) connected to a network management system (NMS) 22. The remote terminal 23 enables a remote maintenance work.
The multiplexer 29 multiplexes the four data signals STM-M supplied thereto into a single high-bit-rate data signal, and adds OHB data thereto. Then, the multiplexer 29 supplies an electro-optic converter (E/O) 34 with the multiplexed data signal with the OHB data added thereto.
The electro-optic converter 34 converts the received electric signal into a corresponding optical signal. Although not shown in FIG. 2, the optical signal outgoing from the electro-optic converter 34 is supplied to the optical coupler 15 shown in FIG. 1, which coupler multiplexes other optical signals generated similarly. Then, the multiplexed optical signal is output from the optical coupler 15 to the optical coupler 17 via the optical fiber cable 16.
An opto-electric (O/E) converter 36 receives the multiplexed optical signal from the optical fiber cable 16. The converter 36 converts the received optical signal into a corresponding electric signal, which is supplied to a demultiplexer (DMUX) 37. The demultiplexer 37 demultiplexes the received signal into the data signals STM-M#1-STM-M#4 and the OHB data. The data signals STM-M#1-STM-M#4 are respectively supplied to devices of the next stage via interface parts 43-46. The OHB data is supplied to a system controller 38, which performs various controls in accordance with instructions supplied from a local terminal 42 or the aforementioned remote terminal 23.
A description will now be given of a transfer of the maintenance information between the communication devices using the OHB data. The wavelength division multiplexing transmission is used in an SDH (Synchronous Digital Hierarchy) optical communication system which conforms to the international standard of synchronous multiplexing recommended by ITU-T. In the SDH optical communication system, the maintenance information is transferred between the communication devices using the OHB data provided in the STM-N frame which is the unit for multiplexing. The way of using the OHB data is defined.
The minimum management interval between the communication devices in the SDH optical communication system is called xe2x80x9csectionxe2x80x9d, and the OHB data for managing the section is called RSOH (Reg. Section Over Head). Conventionally, the RSOH has a section trace function of performing the inter-section management, called J0 byte. The section tracing function using the J0 byte shows from where the signal being transferred comes.
The section trace function will be described with reference to FIG. 4. A station (A) 50 is now located on the transmission side. The optical coupler 15 of the station 50 combines the optical signals respectively having the wavelengths xcex1-xcex4 generated by the line terminal equipment 11-14, and sends the multiplexed signal to a station (B) 51 located on the reception side. The interval between the stations 50 and 51 is the section, and the section trace function using the J0 byte manages information on the section including the country number, the name of the station and the name of the transmitter device
However, in the wavelength division multiplexing transmission system, the J0 bytes of all the wavelength-division-multiplexed signals having different wavelength have the same value because the J0 bytes show from which the respective signals come from (station 50 in the case shown in FIG. 4). Hence, it is impossible to check each of the wavelength-division-multiplexed signals having the different wavelengths by referring to the respective J0 bytes. Conventionally, a spectrum analyzer is used to measure the wavelengths of the wavelength-division-multiplexed signals and check each of them. The above work by the maintenance person is very cumbersome.
In the wavelength division multiplexing transmission system, as an increased number of wavelengths, the adjacent wavelengths become closer to each other. Thus, if a wavelength connection fails, the signals cannot be received correctly or signals other than the target signals may be received. Furthermore, an increased number of wavelengths which are multiplexed and transferred over a single optical fiber needs a more complex management work directed to, for example, getting information on the states of channels.
It is a general object of the present invention to provide a wavelength division multiplexing transmission device and method and a wavelength division multiplexing system, in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a wavelength division multiplexing transmission device, method and system in which each of wavelengths multiplexed and transferred over an optical fiber in the wavelength division multiplexing system can be checked and the wavelength management can be facilitated.
The above objects of the present invention are achieved by a wavelength division multiplexing transmission device comprising: a multiplexer part which multiplexes a plurality of first signals having a first bit rate and different wavelengths into a second signal having a second bit rate higher than the first bit rate and inserts wavelength data information concerning the different wavelengths into the second signal. With the above structure, it is possible to notify a remote device of information indicative of the wavelengths included in the second signal.
The above objects of the present invention are also achieved by a wavelength division multiplexing transmission device comprising: a plurality of multiplexer parts, each of which multiplexes a plurality of first signals having a first bit rate and different wavelengths into a second signal having a second bit rate higher than the first bit rate and inserts wavelength data information concerning the different wavelengths into the second signal; and an optical coupler which combines second signals from the plurality of multiplexer parts and outputs a resultant optical signal.
The above objects of the present invention are also achieved by a wavelength division multiplexing transmission device comprising: a demultiplexer part which demultiplexes a second signal having a second bit rate into first signals having a first bit rate lower than the second bit rate and having different wavelengths and wavelength value data concerning the different wavelengths. With the above structure, it is possible to recognize, on a reception side, which wavelengths are included in the second signal.
The above-mentioned objects of the present invention are achieved by a wavelength division multiplexing transmission device comprising: an optical coupler which separates an optical signal transferred over an optical fiber cable into second signals; and a plurality of demultiplexer parts, each of which demultiplexes one of the second signals having a second bit rate into first signals having a first bit rate lower than the second bit rate and having different wavelengths and wavelength value data concerning the different wavelengths.
The above-mentioned objects of the present invention are also achieved by a wavelength division multiplexing transmission system comprising: a first wavelength division multiplexing transmission device; a second wavelength division multiplexing transmission device; and an optical fiber cable. The first and second wavelength division multiplexing transmission devices are configured as described above.
The above-mentioned objects of the present invention are also achieved by a wavelength division multiplexing transmission method comprising the steps of: multiplexing a plurality of first signals having a first bit rate and different wavelengths into a second signal having a second bit rate higher than the first bit rate; and inserting wavelength data information concerning the different wavelengths into the second signal.
The above-mentioned objects of the present invention are also achieved by a wavelength division multiplexing transmission method comprising the steps of: receiving a second signal; and demultiplexing a second signal having a second bit rate into first signals having a first bit rate lower than the second bit rate and having different wavelengths and wavelength value data concerning the different wavelengths.